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April 27, 2012

Deadly Fungus Causing Dehydration In Wild Frogs

by editor

According to a new study, the fungal infection killing amphibians around the world is causing deadly dehydration in frogs in the wild.

The scientists say that high levels of Batrachochytrium dendrobatidis (Bd), the fungus known as the culprit behind the death of the frogs, disrupts fluid and electrolyte balance in the frogs. As a result, the amphibians' sodium and potassium levels are depleted, causing cardiac arrest and death.

"The mode of death discovered in the lab seems to be what's actually happening in the field, and it's that understanding that is key to doing something about it in the future," he said in a press release.

Vredenburg and colleagues drew blood samples from mountain yellow-legged frogs in 2004, as the chytrid epidemic began sweeping through the basins of the Sierra Nevada range.

Frog populations in Sierra Nevada have been devastated by the outbreak, declining 95 percent after the fungus was first detected in 2004.

"It's been really sad to walk around the basins and think, 'wow, they're really all gone,'" Vredenburg said.

The fungus attacks an amphibian's skin, causing it to become 40 times thicker in some instances. Since frogs depend on their skin to help absorb water, and electrolytes like sodium, they began to become dehydrated because the chytrid disrupts fluid balance in the infected amphibians.

"It's really rare to be able to study physiology in the wild like this, at the exact moment of a disease outbreak," UC Berkeley ecologist Jamie Voyles, the lead author of the study, said. "It's clear that this fungus has a profound effect in the wild."

Sam Scheiner, NSF program officer for EEID, said that wildlife diseases can disrupt human health and economy just as much as agricultural and human diseases.

"Bd has been decimating frog and salamander species worldwide, which may fundamentally disrupt natural systems," Scheiner said in the press release. "This study is an important advance in our understanding of the disease, a first step in finding a way to reduce its effects."

Scientists hope that the findings will help lead to better treatments for the amphibians that are infected.

Voyles said the study suggests that individual frogs being treated for the infection may benefit from having electrolyte supplementation in the advanced stages of the disease.

Researchers are experimenting with different ways of treating individual frogs, like applying anti fungal therapies or inoculating the frogs with bacteria that produces a compound that kills the fungus.

"The disease is not very hard to treat in the lab with antifungals. We know we can treat animals there," Vredenburg said. "But in nature, the disease is still a moving target."

Chytrid has killed off over 200 amphibian species around the world, but Voyles said the new study offers a glimpse of hope that it may be possible to do something to help alleviate the loss of frogs.

The study is published online by peer-reviewed journal PLoS ONE and funded through the joint National Science Foundation and National Institutes of Health program, Ecology and Evolution of Infectious Diseases.